Soak the raisin in warm water for about half an hour. Sift the flour in a big bowl, with the yeast, salt and sugar. Mix to combine well. Drain the raisin and add it to the flour with the chopped rosemary. Pour the water all together in the bowl and quickly mix for a few seconds with your hands or a wooden spoon, until the ingredients come along together. Do not overwork. This step only requires a few seconds. Cover the bowl with a clean cloth and leave to raise in a warm place for 12 to 18 hours. Once the time has passed, use a bit of flour to shape one or two loaf, or even small ones. Leave to raise for 1 hour on a baking tray, then bake it at 250 C for about 30/40 minutes or until golden on top.